The present invention relates to a method for determining a predetermined delay time of a pre-catalytic converter lambda probe in a predetermined arrangement. The invention also relates to a method for determining the oxygen storage capacity of an oxygen store associated with a catalytic converter is part of such predetermined arrangement.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
The predetermined arrangement is directed to an arrangement with an internal combustion engine, wherein the difference between an output signal of the pre-catalytic converter lambda probe and a desired signal is supplied as an input signal to a controller. The controller is typically implemented as a PI controller or PID controller. The output signal of the controller determines the air-fuel ratio of exhaust gas to which the pre-catalytic converter lambda probe is exposed through operation of the internal combustion engine. The output signal determines the quantity of injected fuel and supplied air of the internal combustion engine, which directly determines the air-fuel ratio in the exhaust gas. The delay time to be determined is the time by which an actual air-fuel ratio observed in the output signal of the pre-catalytic converter lambda probe is delayed.
In a predetermined arrangement of the aforedescribed type, the exhaust gas system, which typically includes in the outflow direction of the exhaust gas following the pre-catalytic converter lambda probe a catalytic converter with oxygen storage capability, is typically exposed to exhaust gas by changing the air-fuel ratio λ changes between values greater than one and values less than one, i.e., alternatingly operating rich and lean. This is determined by the desired signal, which forms the basis for forming the difference with the response signal from the pre-catalytic converter lambda probe. Exposure with changing lambda is necessary to systematically compensate for possible errors. The oxygen storage capacity of an oxygen store associated with the catalytic converter is typically determined by filling the oxygen store in a defined manner through exposure to lean exhaust gas following a phase of exposure to rich exhaust gas, where the oxygen store was completely emptied, wherein the quantity of oxygen introduced per unit time is integrated over a time interval. The start of the time interval is typically triggered by the output signal of the pre-catalytic converter lambda probe when this output signal satisfies a predetermined criterion, e.g., crosses a threshold value.
When determining the oxygen storage capacity, the delay in the reaction of the pre-catalytic converter lambda probe to an air-fuel ratio has a direct effect on the measurement values. It is also a general interest to know this delay time.
It would be feasible to set the output signal of the pre-catalytic converter lambda probe in reference to the full signal. However, this simple comparison between “actual” and “desired” provides the correct result only for short delay times. Because the predetermined arrangement includes the controller, the delay in the reaction of the pre-catalytic converter lambda probe causes an immediate overshoot in the output signal of the controller. When the delay reaches a certain magnitude, a type of oscillation is produced where a temporal characteristic is no longer correlated with the aforementioned delay time itself.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for reliably determining the delay time in an arrangement of the aforedescribed type. It would also be desirable and advantageous to determine the oxygen storage capacity of the oxygen store by taking into consideration the determined delay time.